«كَلَوْنَيْ بَيَاضٍ وَصُفْرَةٍ»
Like the two colours white and yellow.
Both belong to the category colour, an intelligible commonality. But estimation may bring them together by emphasizing their divergence or comparison within a particular setting.
One must not assume that whiteness and yellowness are strict logical contradictories in every technical sense. The relevant feature here is their mental comparison or contrast.